Acoustic device



May 7, 1929. T. c. sEDGWEQK 1,?1L697 ACOUSTIC DEVICE Filed Nov: 5, 1927 2 Sheets-Sheet l T. Q. SEDGWIQK ACOUSTIC DEVICE May 7, 19290 Filed Nov, 5, 1927 2 Sheets-Sheet r v m Patented May 7, 1929.

UNITED STATES I 1,711,697 PATENT OFFICE.

THEODORE G. SEDGWICK, OF NEW YORK, N. Y., ASSIGNOR, BY DIRECT AND MESNI ASSIGNMENTS, OF TWO-THIRDS TO TRUMAN FOWLER, F ARLINGTON, NEW JER- SEY.

Application filed November My invention relates to acoustic devices and especiallyv to an acoustic cone of the type adapted to be operated by electromagnetic driving means for sound reproduction.

An important desideratum in the art of electromagnetic sound reproduction, especiallywhere a faithful reproduction. of music distributing meanscapable of responding eflu ficiently and equally well to substantially all frequencies of the audible range Without loss of the tonal qualities or timbre of the origmal and without the addition 'of tonal effects due to resonance of such distributing-means. The

chief object of the present invention is to provide a sound difi'using means of the cone type having the above desired qualities. The present invention attains this object not by rendering the sound emitting member resomm to several frequencies of the audible range, as has heretofore been proposed, but rather by rendering it responsive to and at the same time non-resonant to any of such frequencies, whereby it will reproduce only the impulses imparted to it by the electromagnetic driving means without prolonging or accentuating the vibrations of any particular frequency or frequencies. Another object of the invention is the provision of a method of forming the cone with predetermined operating characteristics.

1 Other objects of the invention will be a parent from a perusal of the following speci I cation and the drawings acompanying the same. 7

In the drawings: Figure 1 is a front view of the finished cone; F Fig. 2 is a side view looking from the left of o Fi 3 is an enlarged scale, detail cross sectioga view taken on the line 33 of Fig. 1; an

Fig. 4 is a diagram showing the method of forming the blank or surface development of the cone.

, Referring to the drawings in detail, and first to Figs. 1 to 3, the cone surface member or cone 1, of special heart-shaped form to be later described, is mounted on a spider frame 2 of similar shape,-the cone being secured to the frame by a clamping flange 3 (Fig. 4) clamped to the frame within the recess 4 by an overlying clamping plate 5 with an interposed padding 6 of felt, rubber or other suitable padding material. The clamping flange ACOUSTIC DEVICE.

5, 1927. Serial No. 231,337?

below this line free, ample freedom being assured by the space between the free edge and the frame determined by thethickness of the padding 6 below the flange 3 which padding or speech is desired,.is a sound diffusing or ing plate and flange, that is to'the line A-- the free edge of the cone sloping awa from the frame below the line AB. paced clamping screws 7 adj ustably secure the plate 5 to the frame, enabling the clamping pressure to be adjusted to procure thebest operating condition. I

A mounting post or pedestal 8 extends from the hub portion 9 of the frame toward the apex of the cone and on this pedestal is mounted an electromagnetic driving unit 10 of any known or other suitable form with its connecting rod or driving stylus 11 connected to the apex of the cone in a line concentric with the cone axis, that is, bisecting the angles formed by diametrically opposite cone elements 01' radii. A pair-of eyelets 12 is provided on extends downwardly only as far as the clampeither side of the frame to enable it to be hung on a wall by a suitable cord not shown, the

spacing lugs 13 projectingfrom the back of the frame acting to space it away from the wall. Obviously, in lieu of the hanging or wall support, the frame may be supported on a stand or pedestal as by securing the hub portion 9 to the top of the pedestal.

The shape of the cone 1, which is an important feature of the invention, is such that the cone elements or cone-surface radii vary in length at aconstant or uniform rate with the ratio of the longest radius to the diametrical- 1y opposite (shortest) radius equalto other than an even fraction and preferably very slightly less than some ratio of even fraction, for example slightly less than 3 to 1. That is, the natural wave length along the shorter radius should not equal any harmonic of the natural wave along the longer radius. This results in preventing harmonic vibrations from being set up along this diameter. While due to the constant increase of one and decrease-of the other of diametrically opposite radii, there will be diametriclines on which they will have a ratio equal to a'harmonic such as l to 2, there will be no sector of appreciable To form a cone having the above characteristics the cone surface is develo ed in a plane as indicated in Fig. 4, where t e spiral curve shown is a graph of the equation =R plotted in polar coordinates, Where 0 equals the angle of rotation and. R=.the radius in units of length numerically equal to 0.

Starting with the line A-O as the zero position of a' line rotating counterclockwise about the point 0 and increasing, from zero length,

one unit length for each degree of rotation, at a position degrees removed from the 82 30 which is spaced half way between two adjacent 15 degree radii. It is a section of this curve that is used todefine the edges or rim of opposite sides of the cone. To form one of the symmetrical halves of the cone,'a section must bechosen which lies between two radii less than 180 de ees apart and these two radii brought into t e plane of the axis to example b form the'diametrically opposite, longest and shortest, radii of the cone lyin on the mid line C-D (Fig. 1). To have t eseradii in non-harmonic relation I choose a ratio which may be any decimal figure provided it does not interfere with the proposition that there should be no radii equal to an even fraction. In the present instance, the ratio of 2.91 is used'because it is found to substantially fulfill the requirements mentioned. This ratio is obtained by using that segment of the'spiral figure (Fig. 4) lying tothe right between the radii of 240 and 82 30'. that as each radius is equal numerically to the number of degrees their ratio will be as 240 is to 82 or which reduces decimally to 2.91. Thus the ratio is'slightly short of the third harmonic. By duplicating this sector on the left side of the 240 radius with the 240 radii coinciding, the two 82 30' radii will be 45 apart thus forming a surface development which may be formed into a cone by bringing together the two edges of the sectors defined by the two 82 30' radii to form the cone of Fig. 1. In cutting the actual blank allowance is of course made for the clamping flange 3 outside the curve as indicated in dotted lines at 3 in Fig. 4. The joining of the short radial edges maybe effected in any known or other suitable manner, for overlapping, allowance being made for t e overlap in the forming of the blank or surface development.

As the shape of the cone is of the essence of the invention, it is to be understood that the O the line will equal 0-, or 30' units of length, at60 degrees it will equal It will be clear cone may be fabricated in an manner resultmg in a cone of the shape escribed, as for example by molding or blocking.

It is also to beunderstood that while I have herein shown and described a particular embodiment of myinvention for the sake of disclosure, the invention is not limited to cone surface member of varying radius, all

ortions having a radius above a iven value ing fixed at the edges and a 1 portions having a radius below said given value being free at the edges. v,

3. A sound functioning conec'ompi-ising a cone surface member having a radius of con-' stant variation and a corresponding constant variation of the radial distance of the center of gravity of successive infinitesimal sectors. 4. A sound functionin cone comprising a cone surface member having a portion of long radius and a portion of short radius, the lon radius portion being fixed at the edge and the short radius portion being free at the edge. 5. A sound functioning cone comprising a cone surface member the radial elements of which on each side of a median plane have their extremities at a varyin distance from the apex, varying one unit in ength for each degree of rotation.

6. A sound functioning cone comprising a cone surface member having two portions one a continuous portion of long radlus an the other a continuous portion of short radius, the portion of long radius being damped and the portion of short radius being un damped.

7. A sound functionin cone comprisin a cone surface member of a shape such t at there is but one position where the radii 180 degrees apart have a given even ratio.

8. A sound functioning cone comprising a cone surface member having each half formed from a portion of a spiral subtended between radii less than 180 apart and having a rat-i0 of approximately 1 to 2.91;

9. A sound functioning cone comprising a cone surface member having the longest one of each pair of diametrically opposite radial elements damped.

10. The method of forming an acoustic cone from a piece of sheet material which consists in laying off a spiral curve havin a radius uniformly increasing from zero ength to one unit length for each degree of rotation,

to an extent sufficient toinclude the portion lying between the 82 30 radius and the 240 radius, choosing the sector lying between these radii and laying a second sector symmetrical to the first with its center and its 240 radius coinciding with that of the first, and securing the two 82 30' radii together to form acone.

11. The method of forming an accoustic cone from a piece of sheet material which comprises choosing a sector less than 180 of a spiral lying between two radii having a ratio other than an even fraction, laying off on the sheet material two such similar sectors symmetrically on opposite sides of a center line with their centers and longest radial edges coinciding on the line, and bringing the two shortest radial edges together to form a cone.

12. The method of forming an acoustic cone from a piece of sheet material which comprises choosing a sector less than 180 of a spiral lying between two radii having a ratio other than an even fraction, laying off on the sheet material two such similar sectors symmetrically on. opposite sides of a center linewiththeircenters and longest radial edges coinciding onthe line, cutting out the material along the line of the heart-shaped figure thus formed leaving an extended flange portion around a portion of the edge determining the longer radii, bringing the two shortest radial edges together to form a cone, and bending the flange portion at an angle to the cone surface to terminate the cone surface at the line of the spiral.

13. A sound functioning cone comprising a cone surface member having each half formed from a portion of a spiral subtended between radii less than 180 apart and having a ratio other than an even fraction.

In testimony whereof I affix my signature.

THEODORE o. SEDGWIIOK. 

